A liquid crystal display (LCD) device is a device which performs display in such a manner that the optical property of light emitted from a light source is controlled by using a liquid crystal layer, and the like, filled between a pair of substrates, and is used in various fields by taking advantage of its features, such as thin profile, light weight and low power consumption.
In the liquid crystal display device, an alignment state of liquid crystal molecules is changed by applying a voltage to the liquid crystal layer by using a pair of electrodes formed on the substrates, and thereby a polarization state of the light passing through the liquid crystal layer is changed. In the liquid crystal display device, color filters of a plurality of colors are arranged to perform color display. The pair of substrates sandwiching the liquid crystal layer are held by spacers so as to have a uniform gap (cell gap) therebetween and are bonded to each other by a sealing material.
In the liquid crystal display device, sub-pixels of three colors of red (R), green (G) and blue (B) are usually formed. A color filter of each color is arranged for each of the sub-pixels, and color control is performed for each pixel by adjusting light passing through the color filter of each color.
In recent years, there has been made such a contrivance that, in addition to the RGB sub-pixels, a white (W) sub-pixel is arranged in order to increase luminance (see, for example, Patent Literature 1). Further, a method has also been investigated in which the areas of the RGBW sub-pixels are made different for each color so as to suitably adjust color balance (see, for example, Patent Literature 2).
In the liquid crystal display device, pixel electrodes are usually arranged in a matrix form, and each of the pixel electrodes is driven through a switch formed by a thin film transistor (TFT). The TFT is a three terminal field-effect transistor, and a drain electrode of each of the TFTs is connected to the pixel electrode corresponding to the TFT. A gate electrode of each of the TFTs is connected to a gate bus line of each row of the matrix. A source electrode of each of the TFTs is connected to a source bus line of each column of the matrix. A desired image can be obtained by applying an image signal to the source bus line and by sequentially scanning the gate bus line.
Some of the liquid crystal display devices have a multi-gap configuration in which a thickness (cell gap) of the liquid crystal layer is made different for the sub-pixel of each color. However, in the case where a size of the cell gap is made different, a value of capacitance associated with the pixel electrode is changed. Therefore, in order to eliminate the difference in the pixel capacitance between the sub-pixels, it is necessary to make contrivances such as (a) equalizing pixel electrode areas between the sub-pixels and making storage capacitance different for each of the sub-pixels or (b) making the pixel electrode areas different for each of the sub-pixels and equalizing the storage capacitance between the sub-pixels (see, for example, Patent Literature 3).
Further, in the liquid crystal display device, in order to solve a viewing angle dependency problem due to a difference in γ characteristics between the time when the display is viewed in a front direction and the time when the display is viewed in an oblique direction, there is a case where a pixel is divided into a plurality of sub-pixels, and where the γ characteristics are made close to each other (see, for example, Patent Literature 4). The γ characteristics mean gradation dependency of display luminance. That the γ characteristics are different between the time when the display is viewed in the front direction and the time when the display is viewed in the oblique direction means that a gradation display state is changed according to the observation direction. The viewing angle dependency problem due to the γ characteristics can be eliminated in such a manner that a state having different γ characteristics is formed by applying a different voltage to the liquid crystal layer corresponding to each of the sub-pixels.
Further, as a method for forming a spacer, a method has also been tried in which, when color filters are formed in correspondence with RGB sub-pixels, the color filters are also similarly formed at a place where the spacer is to be formed, and are laminated to form the spacer (see, for example, Patent Literature 5). In Patent Literature 5, in order to compensate a change in the capacitance of each pixel due to the spacer formed in the sub-pixel, a method has been investigated which equalizes a capacitance ratio of each of the respective pixels by changing a size of storage capacitor line.
Moreover, an active matrix substrate is disclosed in which a common electrode line is formed parallel to a scanning signal line, and each pixel circuit is formed so that the capacity Cgd between the scanning signal line and the pixel electrode becomes greater as electrically going farther from the scanning signal line drive circuit, in order to eliminate non-uniformity of the level shift of pixel potential generated at the scan signal fall (for example, Patent Literature 6).